British authorities say horse meat containing a veterinarian's drug that could potentially be harmful to humans might have entered the food chain in France.

Eight horses slaughtered in Britain have tested positive for phenylbutazone, or bute, which is banned for horses meant for human consumption.

Britain's Food Standards Authority says meat from six of those horses was sent to France and could have ended up on shelves sold as beef.

But the UK's chief medical officer has sought to reassure consumers, saying bute poses a limited public health risk.

A British parliamentary report into the widening horse meat scandal says current discoveries are likely to be the "tip of the iceberg".

Overnight British police arrested three men suspected of passing horse meat off as beef on suspicion of fraud.

Two men were arrested in Aberystwyth on the west coast of Wales where a food processing plant is based, and one was detained in West Yorkshire in northern England, where police raided a slaughterhouse on Tuesday.

Both the processing plant and the slaughterhouse were shut down by Britain's Food Standards Agency on Wednesday.

They are the first two plants in Britain accused of selling horse meat labelled as beef.

Meanwhile, French investigators say meat processing company Spanghero knowingly sold around 750 tonnes of horse meat as beef.

Facts about phenylbutazone

Better known as bute, it is a painkiller for horses

In high doses it can cause blood disorders in humans

Was used in the 1950s to treat arthritis and gout in humans

It has since been withdrawn from pharmacy shelves

It is banned for use in food-producing animals, including dairy cows

The French government is suspending the company's licence to handle meat while investigations are carried out.

The falsely labelled meat was sent to French firm Comigel, which makes frozen food at its Tavola factory in Luxembourg.

Consumer affairs minister Benoit Hamon says Spanghero will be prosecuted over the "fraud".

But Spanghero has denied any wrongdoing, saying in a statement that it had never ordered, received or resold any meat that it did not believe to be beef.

In Britain, three men have been arrested on suspicion of passing horse meat off as beef.

Concerns about horsemeat first emerged in mid-January when Irish authorities found traces of horse in beefburgers made by firms in the Ireland and Britain and the UK and sold in supermarket chains including Tesco and Aldi.

The discovery has sparked a European crisis, with supermarkets across the continent withdrawing millions of beef products.

Moscow's words and actions — including the alleged poisoning of a former spy — are not the results of random aggression but rather fall into distinct patterns that can help us anticipate Russia's next moves under Vladimir Putin.